Conventional air load exercise devices presently offer several advantages over friction resistance devices which typically use pads or belts to apply a load. Air load devices offer a smoother resistance by eliminating the need for frictional contact between parts, thus also reducing the number of wearing parts. Air load devices are also simpler to calibrate for workload because of the known exponential relationship between revolutions per minute of the fan wheel and the corresponding load. Air load devices are distinct from all other load applying devices in that a by-product of the user's work is moving air which is effective for cooling. The cooling effect of this self-generated wind greatly enhances the potential work output of the user and also provides a more comfortable environment in which to exercise. By making exercise more comfortable, a user is more likely to workout longer and to continue with a given exercise program.
Conventional air load exercise devices have several deficencies, however. Because load increases with increased rpm of the resistance wheel, the user is restricted to a narrow cadence or stroke speed range. For example, if one user of an air load exercycle wishes to pedal at his normal outdoor cycling cadence of 100 rpm, he would have to work significantly harder than another user of the same machine who chooses to pedal at his normal cadence of 55 rpm. In fact, these two users would not be able to use the same conventional air load exercycle at their respective cadences. Related to this problem is the fact that some air load resistance machines cannot accommodate users of a wide range of physical conditions because of the limited adjustability in load. Athletes who are interested in developing sport-specific muscles should be able to select a cadence or stroke that more accurately replicates the cadence or stroke they use in their sport. A football player using a step machine might want to develop power muscles by working at high load and low speed, while a cross country runner might want to develop endurance muscles by working at lower loads and higher speeds. A conventional air load machine does not accomodate the divergent needs to these two users.
Finally, a conventional air load machine cannot be combined with an interactive microprocessor to vary the load level according to a preprogrammed course or time, or according to the heart rate of the user. An interactive exercise device is often more interesting to use; it pushes the user to higher workout levels; and, when heart rate is one of the input parameters, it provides a more effective and safer workout.
There are several known magnetically variable load exercise devices. These, like the air load devices, are frictionless. Unlike the air load devices, the magnetic devices provide the advantage of a variable load. They however do not provide moving air with its highly desirable cooling effect. Users of the known magnetically loaded devices therefore suffer the output limiting effects of heat stress, and they perform at lower levels than they would be capable of in a cooling environment of moving air.
Some of the magnetically variable load devices use an electromagnet to vary the load. This requires an electrical power source which may not always be convenient to the user. It also adds to complexity and cost of the equipment. Other magnetic variable load devices use small diameter eddy current discs which carry little momentum, and therefore have an uneven pulsating feel, especially at high load levels. Eddy current devices also generate a considerable amount of Joule heat as a by-product of the resistance the magnets provide. The elevated temperature levels of the eddy current discs and nearby magnets can reduce the amount of resistance being applied. The user may experience inconsistent load levels and, when used in ergometric machines, inaccurate readouts of workload levels.
Variable magnetic loading devices are disclosed in U.S. Pat. Nos.: 4,152,617 to Janson; 4,752,066 to Housayama; and 4,775,145 to Tsuyama.